The Carboxyl Transferase Component of Acetyl CoA Carboxylase: Structural Evidence for Intersubunit Translocation of the Biotin Prosthetic Group

AUTOR(ES)

Guchhait, Ras B.

RESUMO

An essential protein component of acetyl CoA carboxylase, isolated and extensively purified from cell-free extracts of Escherichia coli, has been identified as malonyl CoA: d-biotin carboxyl transferase. This enzyme, which does not contain covalently-bound biotin, catalyzes carboxyl transfer from malonyl CoA to free d-biotin, a model reaction for the second step in the carboxylation of acetyl CoA. The transcarboxylation product, after stabilization by methylation, was identified as 1′-N-carboxy-d-biotin dimethyl ester. These results indicate the presence of a biotin site on the carboxyl transferase, distinct from that on the biotin carboxylase, which carries out the first step in the overall process. In addition, the carboxyl transferase catalyzes a slower abortive decarboxylation of malonyl CoA, thus indicating that carboxyl abstraction and protonation do not require the participation of biotin.

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